1. Field of the Invention
The present invention concerns new and novel fingernail cosmetic coatings, more specifically water-based fingernail cosmetic coatings, which are unlike organic solvent-based fingernail cosmetic coatings in that a major part of the volatile content is water.
At the present time, commercial fingernail cosmetic coatings are generally of the organic solvent-based type, consisting primarily of a film-forming agent, such as nitrocellulose and alkyd or polyester resin, plus plasticizers and organic solvents. Although these organic solvent-based, fingernail cosmetic coatings have excellent film-forming properties, they also have serious drawbacks due to the inclusion of large amounts of organic solvents. These drawbacks include inflammability, very high Volatile Organic Content (5-7 pounds per gallon), strong and irritating solvent odor, and adverse effects on the human body, particularly on the nails and skin.
The Volatile Organic Content (VOC) of a coating is a measure of the total amount of organic solvent and other volatile substances which can be emitted to the atmosphere by the coating. It is expressed in units of pounds of volatile organic matter per gallon of coating, and, since water is an exempt solvent, for any given sample of coating it can be calculated by means of the following equation: ##EQU1##
2. Description of the Related Art
In order to overcome these drawbacks, aqueous fingernail coatings, in which the content of volatile organic compounds is considerably lower than in the organic solvent-based type, have been developed and disclosed. For example, Japanese Unexamined Patent Publications (Kokai) Nos. 54-28836 and 54-52736 and Japanese Examined Patent Publication (Kokoku) No. 55-43445 disclose aqueous fingernail coatings containing specified acrylic polymer emulsions, but coatings made according to these inventions are difficult to apply by brush and have poor film-forming ability, and the dried films have poor gloss and poor adhesion to fingernails. Japanese Unexamined Patent Publications (Kokai) Nos. 56-131513 and 57-56410 disclose aqueous fingernail coatings containing specified acrylic polymer microemulsions, but a drawback of the dry films from coatings made according to the latter two inventions is their extreme brittleness under mechanical wear, resulting in flaking or chipping of the films from the fingernails.
Yamazaki et al. (U.S. Pat. No. 4,897,261) discloses a fingernail cosmetic composition containing at least one resin and at least one organic solvent, characterized by incorporating therein water and a water-incorporating compound having at least one hydrophilic moiety, and, if desired, a moisturizing agent and a fragrance-containing agent. It is specified therein that the water-incorporating compound which may be used in the invention is, for example, a water-soluble polymer, an oil-soluble polymer, or a surface-active agent. However, it is clearly stated therein that, in the fingernail composition of the invention, water and the water-incorporating compound are incorporated as an internal phase of a water-in-oil emulsion, and, more particularly, the resins and organic solvents form a continuous external phase of an oil phase, and an aqueous phase is dispersed therein as the internal phase in the form of small particles (U.S. Pat. No. 4,897,261, Abstract, col.3, lines 29-35). Furthermore, Yamzaki et al. claims that the composition covered contains 0.5 to 30% of water based on the total weight of the composition (ibid., Claim No.1, col. 19, lines 42-45), and, in addition, they state, "A composition containing more than 30% by weight of water is not desirable" (ibid., Abstract, col. 3, lines 43-44).
The present invention does not fall under the claims or disclosures of U.S. Pat. No. 4,897,261 (Yamazaki et al.), as the latter includes only water-in-oil emulsions, whereas the present invention includes only resin-in-water emulsions, the resin corresponding to the "oil" or hydrophobic constituent of the Yamazaki et al. patent.
Furthermore, U.S. Pat. No. 4,897,261 encompasses only compositions containing 0.5 to 30% of water based on the total weight of the composition (Claim No. 1, col.19, lines 42-45, and Abstract, col. 3, lines 36-39), whereas compositions encompassed by application Ser. No. 08/778,694 contain 40-70% of water based on the total weight of the composition.
Yamazaki et al. does not teach specifically that the composition must contain a thickener,but some of the water-soluble and oil-soluble polymers which are listed therein may act as thickeners. However, none of the polymers which are cited therein are associative thickeners, while the inclusion of an associative type of thickener is essential in the composition taught by application Ser. No. 08/778,694. Associative thickeners are characterized by the fact that they have in their molecules hydrophobic (water-repellant) segments or blocks attached to the hydrophilic (water-attractive) segments. They thicken by means of a secondary valency association with other hydrophobic groups on other components of the composition, such as resins and pigments. The secondary valence association is broken when subjected to a high shearing stress, such as occurs during application of the composition by brushing. Associative thickeners, therefore, can provide effective thickening and anti-settling properties while the composition is at rest in a container, but permit good flow and leveling during application by brushing.